At present, cryogenic fluids find use in numerous and various fields of industry. Thus, nitrogen, helium, neon, argon, deuterium, krypton, and xenon are at present used in the electronic field.
This field especially requires these compounds to be as pure as possible, which is to say stripped of most of their impurities, so as to avoid subsequent degradation of the electronic components by reaction with said impurities. By way of example, can be cited the use of ultra pure helium, as inert gas utilizable in constant temperature control of the support chips for integrated circuits forming memories or processors, or in the cooling of "wafers".
There is also an increase in demand in the electronic field as to the supply of ultra pure hydrogen.
Numerous processes for purification of cryogenic fluids, such as inert fluids, are known from the prior art, but these latter generally have several drawbacks or disadvantages, namely:
they are not suitable for purification of cryogenic fluids no matter what their state, namely liquid, gas, supercritical and/or diphase, and therefore require heating and/or cooling steps, as the case may be, to bring the cryogenic fluid to be purified to a given temperature, at which the elimination of the impurities can be carried out; PA1 they require the use of costly adsorbents, for example of the getter type; PA1 the adsorbents used are not effective unless "hot", that is, at temperatures higher than 0.degree. C., even at 100.degree. C.; PA1 they are limited as to the quantity of cryogenic fluid that can be treated during a given period of time; PA1 they are limited to one type of cryogenic fluid, for example argon or helium, which is to say that the same process and/or the same device cannot be used to purify cryogenic fluids of different types; PA1 they are limited as to the impurities that can be eliminated by the use of adsorbents or catalysts which react only in a selective manner, which is to say with certain impurities and not others, with the result that a cryogenic fluid is only partially purified; for example, the conventional adsorbents or catalysts do not permit eliminating nitrogen impurities contained in helium. PA1 they generally comprise one or several oxidative catalytic steps so as to convert particularly the hydrogen and/or carbon monoxide impurities into water and/or carbon dioxide. PA1 a step of mechanical filtration of at least one impurity in solid state, PA1 and a step of adsorption of at least one impurity in liquid or gaseous state, PA1 and in which there is recovered at least a portion of the cryogenic fluid at least partially purified. PA1 In other words, the impurities in solid state (crystalline) contained in the cryogenic fluid to be purified are retained by mechanical filtration, whilst the impurities in liquid or in gaseous phase are adsorbed b, means of at least one adsorbent material. PA1 the cryogenic fluid is such that its boiling point Pe is less than -100.degree. C., preferably less than -150.degree. C., more preferably below -240.degree. C. (at a pressure of 10.sup.5 Pa); PA1 the cryogenic fluid to be purified is selected from the group comprised by helium, hydrogen, deuterium (D.sub.2), krypton, xenon, neon and argon (there is understood by helium: helium and its isotopes He.sup.3 and He.sup.4) PA1 the cryogenic fluid to be purified is helium and the eliminated impurities are from the group comprised by hydrogen, neon, nitrogen, carbon monoxide, carbon dioxide, oxygen, argon, xenon, krypton, hydrocarbons and water; PA1 the cryogenic fluid to be purified is hydrogen and the impurities are from the group comprised by neon, nitrogen, carbon monoxide, carbon dioxide, oxygen, argon, xenon, krypton, hydrocarbons and water; PA1 the cryogenic fluid to be purified is neon and the impurities are from the group comprised by nitrogen, carbon monoxide, carbon dioxide, oxygen, argon, xenon, krypton, hydrocarbons and water; PA1 the mechanical filtration carried out by means of a metal or ceramic filter, or by means of adsorbent material used to eliminate impurities in the liquid or gaseous state. Thus, said adsorbent material can also serve as a filter so as to retain the particles and solid impurities (crystalline) contained in the cryogenic fluid to be purified; in this case, the steps of filtration and adsorption will be simultaneous. PA1 the adsorption of the impurities is carried out by means of an adsorbent chosen from the group comprised by active carbon, zeolites, silica gel or any other porous adsorbent permitting retaining effectively one or several types of soluble or gaseous impurities in the cryogenic fluid to be purified, for example, a carbon cloth. PA1 at least one mechanical filtration step is carried out upstream and/or downstream of at least one adsorption step and, preferably, upstream and downstream of the adsorption step. It is also possible to alternate several adsorption steps and several steps of filtration by using identical adsorption materials and filtration means, analogous or different in the different steps. PA1 the adsorbent used in the adsorption step of the impurities contained in the cryogenic fluid is subjected to at least one step of regeneration. This regeneration of the adsorbent material can be carried out for example by the following operative procedure: PA1 stoving for several hours at a temperature of 100.degree. C. to 150.degree. C. of the adsorbent material, such as active carbon (only during the first use of the adsorbent material); PA1 sweeping or purging the purifier with the help of an inert gas such as nitrogen, at ambient temperature and at atmospheric pressure; PA1 and subsequently sweeping with the aid of the gas to be purified at ambient temperature and at atmospheric pressure. PA1 storage means for the purified cryogenic fluid; PA1 conduit means for bringing the purified cryogenic fluid to a utilization site; PA1 means for regenerating the adsorbent material, permitting regeneration of said adsorbent material, for example according to the operative condition mentioned above. PA1 liquid or cooled, which is to say at a temperature below its boiling point, PA1 gaseous, which is to say at a temperature higher by several degrees than its liquefaction temperature or boiling point, for example being at a temperature between 5.degree. C. and 20.degree. C. above its boiling point. PA1 diphasic, which is to say in the form of a liquid/gas mixture, hence at a temperature substantially equal to the boiling point, or fluctuating about said boiling point, PA1 or supercritical, for example in the case of helium, at a temperature of about -268.degree. C. for a pressure of 2,275.10.sup.5 Pa.
Thus, U.S. Pat. No. 3,996,082 discloses a process for the purification of gaseous argon from its oxygen impurity by means of a synthetic zeolite of type A.
U.S. Pat. No. 2,874,030 discloses itself a process for the purification of gaseous argon from its oxygen impurity, in which the oxygen is transformed into water by catalytic reaction with excess hydrogen; the water formed being then eliminated by dehydration.
EP-A-0,350,656 discloses moreover a process for the purification of an inert gas of its oxygen, carbon monoxide and hydrogen impurities, in which the carbon monoxide and the hydrogen are eliminated by catalytic oxidation at a temperature comprised between 150.degree. C. and 250.degree. C. in the presence of a first reduced copper-based catalyst, then a second oxidized copper-based catalyst, giving carbon dioxide and water, which are then eliminated by adsorption at ambient temperature on an adsorbent of the molecular sieve type.
Moreover, FR 9604955 discloses a process to supply a utilization conduit with ultra pure helium, in which helium is withdrawn in liquid phase or in supercritical phase from a storage reservoir, the helium is filtered by means of a steel cloth so as to retain solid impurities, the filtered helium is vaporized and is sent to the utilization conduit. It is recited in this document that the hydrogen and/or neon impurities dissolved in the liquid or supercritical helium are not retained.
FR 9507943 discloses itself a process of purification of inert gases, such as nitrogen and rare gases, of their oxygen and carbon monoxide impurities, by adsorption at a temperature below 30.degree. C. on a specific adsorbent of the porous metallic oxide type; the hydrogen impurity is then eliminated by distillation.
Moreover, FR 9611271 relates to the purification of a cryogenic fluid, such as liquid nitrogen, liquid argon or liquid helium, of its hydrogen, carbon monoxide and/or oxygen impurities, by adsorption on a support of the type of alumina, silica, zeolite or titanium oxides supporting a metal, such as platinum, palladium, rhodium or iridium.
Moreover, U.S. Pat. No. 4,659,351 discloses a process in two steps for obtaining liquid helium, in which a gaseous flow consisting essentially of helium and nitrogen with several minor impurities is subjected to a cooling step so as to condense said minor impurities and nitrogen, which are then eliminated; the gaseous flow enriched in helium is then subjected to a PSA type process (pressure swing adsorption) or a process of adsorption by pressure variation, from which results a flow of relatively pure gaseous helium, which helium is then condensed to liquid helium. It will be easily understood that this process has numerous disadvantages and drawbacks, not only as to the cost of energy but also as to the purity of helium obtained. Thus, the requirement to use the steps of vaporization/liquefaction of helium is very costly from a point of view of energy and finance, and although the helium obtained will be relatively pure, it contains quantities of impurities too high to be used particularly for electronics.